Laryngeal muscles perform a variety of functions including sound production, glottis opening during inspiration, and airway protection. We propose to determine if and how laryngeal motor units are specialized with respect to these functions. Using a novel method for stimulating and recording from intact laryngeal motoneurons in anesthetized monkeys, we intend to characterize individual motor units according to: 1) the functions they mediate, 2) their positions in the recruitment sequence for each function, 3) their axon conduction velocities, 4) and their muscle fiber contractile properties. At the termination of each experiment, the muscle fiber histochemistry of a motor unit so characterized will be revealed using a glycogen depletion paradigm. The location and morphology of its cell body in the brainstem can also be ascertained following HRP iontophoresis into its axon. After classifying laryngeal motor units with respect to these characteristics, a second set of experiments will be conducted on awake monkeys. In these experiments we propose to record from laryngeal motoneurons using a brainstem approach with extracellular microelectrodes 1) to identify the classes of motor units involved in vocalization, 2) to determine their recruitment order, 3) to identify with retrograde and anterograde tracing techniques those brain structures having connections with these and other physiologically described laryngeal motoneurons. These studies will help provide a foundation for understanding the nature of the brainstem control of laryngeal muscles during sound production in man.